Device and method for asymmetrical thermal therapy with helical dipole microwave antenna

ABSTRACT

An intraurethral, Foley-type catheter shaft contains a microwave antenna capable of generating a cylindrically symmetrical thermal pattern, within which temperatures are capable of exceeding 45° C. The antenna, which is positioned within the shaft, is surrounded by means within the shaft for absorbing thermal energy conducted by the tissue and asymmetrically absorbing electromagnetic energy emitted by the antenna--a greater amount of electromagnetic energy being absorbed on one side of the shaft. This asymmetrical absorption alters the thermal pattern generated by the microwave antenna, making it cylindrically asymmetrical, which effectively focuses microwave thermal therapy toward undesirous benign tumorous tissue growth of a prostate anterior and lateral to the urethra, and away from healthy tissue posterior to the urethra.

This is a continuation of application Ser. No. 07/847,718, filed Mar. 6,1992.

REFERENCE TO CO-PENDING APPLICATIONS

Reference is made to the following co-pending U.S. Patent applicationSer. No. 07/847,915, filed Mar. 6, 1992, entitled GAMMA MATCHED, HELICALDIPOLE MICROWAVE ANTENNA, by E. Rudie, and Ser. No. 07/847,894, filedMar. 6, 1992, entitled METHOD FOR TREATING INTERSTITIAL TISSUEASSOCIATED WITH MICROWAVE THERMAL THERAPY, by B. Neilson et al.

BACKGROUND OF THE INVENTION

The present invention relates to the field of microwave thermal therapyof tissue. In particular, the present invention relates to a catheterfor transurethral microwave thermal therapy of benign prostatichyperplasia (BPH).

The prostate gland is a complex, chestnut-shaped organ which encirclesthe urethra immediately below the bladder. Nearly one third of theprostate tissue anterior to the urethra consists of fibromuscular tissuethat is anatomically and functionally related to the urethra andbladder. The remaining two thirds of the prostate is generally posteriorto the urethra and is comprised of glandular tissue.

This relatively small organ, which is the most frequently diseased ofall internal organs, is the site of a common affliction among older men:BPH (benign prostatic hyperplasia). BPH is a nonmalignant, bilateralnodular expansion of prostrate tissue in the transition zone, aperiurethral region of the prostate between the fibromuscular tissue andthe glandular tissue. The degree of nodular expansion within thetransition zone tends to be greatest anterior and lateral to theurethra, relative to the posterior-most region of the urethra. Leftuntreated, BPH causes obstruction of the urethra which usually resultsin increased urinary frequency, urgency, incontinence, nocturia and slowor interrupted urinary stream. BPH may also result in more severecomplications, such as urinary tract infection, acute urinary retention,hydronephrosis and uraemia.

Traditionally, the most frequent treatment for BPH has been surgery(transurethral resection). Surgery, however, is often not an availablemethod of treatment for a variety of reasons. First, due to the advancedage of many patients with BPH, other health problems, such ascardiovascular disease, can warrant against surgical intervention.Second, potential complications associated with transurethral surgery,such as hemorrhage, anesthetic complications, urinary infection,dysuria, incontinence and retrograde ejaculation, can adversely affect apatient's willingness to undergo such a procedure.

A fairly recent alternative treatment method for BPH involves microwavethermal therapy, in which microwave energy is employed to elevate thetemperature of tissue surrounding the prostatic urethra above about 45°C., thereby thermally damaging the tumorous tissue. Delivery ofmicrowave energy to tumorous prostatic tissue is generally accomplishedby a microwave antenna-containing applicator, which is positioned withina body cavity adjacent the prostate gland. The microwave antenna, whenenergized, heats adjacent tissue due to molecular excitation andgenerates a cylindrically symmetrical radiation pattern whichencompasses and necroses the tumorous prostatic tissue. The necrosedintraprostatic tissue is subsequently reabsorbed by the body, therebyrelieving an individual from the symptoms of BPH.

One method of microwave thermal therapy described in the art includesintrarectal insertion of a microwave antenna-containing applicator. Heatgenerated by the antenna's electromagnetic field is monitored by asensor which is positioned near the prostate gland by a urethralcatheter. Owing to the distance between the rectum and the tumorousprostatic tissue of the transition zone, however, healthy interveningtissue within the cylindrically symmetrical radiation pattern is alsodamaged in the course of the intrarectal treatment. Intrarectalmicrowave thermal therapy applicators are described in the followingreferences: Eshel et al. U.S. Pat. No. 4,813,429; and, A. Yerushalmi etal., Localized Deep Microwave Hyperthermia in the Treatment of PoorOperative Risk patients with Benign Prostatic Hyperplasia, 133 JOURNALOF UROLOGY 873 (1985).

A safer and more efficacious treatment of BPH is transurethral microwavethermal therapy. This method of treatment minimizes the distance betweena microwave antenna-containing applicator and the transition zone of theprostate by positioning a Foley-type catheter-bearing applicatoradjacent to the prostate gland within the urethra. Due to the closeproximity of the microwave antenna to the prostate, a lesser volume oftissue is exposed to the cylindrically symmetrical radiation patterngenerated by the microwave antenna, and the amount of healthy tissuenecrosed is reduced. Intraurethral applicators of the type described canbe found in Turner et al. U.S. Pat. No. 4,967,765 and Hascoet et al.European Patent Application 89403199.6.

While the close proximity of a transurethral microwave thermal therapyapplicator to prostatic tissue reduces the amount of damage to healthytissue, controlling the volume of tissue to be affected by the microwaveenergy field continues to be problematic. For instance, microwaveantennas known in the art have tended to produce electromagnetic fieldswhich affect a volume of tissue, beyond the desired area of treatment,which necroses healthy, normal tissue.

SUMMARY OF THE INVENTION

The present invention is based upon the recognition that in patientssuffering from BPH, tumorous tissue growth within the prostate tends tobe the greatest in the portion of the transition zone anterior andlateral to the urethra. The present invention is a transurethral thermaltherapy catheter for thermal treatment of BPH which is capable ofselectively directing microwave energy toward tumorous prostatic tissuegrowth anterior and lateral to the urethra, while sparing the urethraand healthy tissue posterior to the urethra from thermal damage.

The catheter preferably includes a flexible shaft which contains amultiplicity of lumens that extend the length of the shaft. A relativelylarge lumen is located eccentric to a longitudinal axis of the shaft,near a first side of the shaft, and is provided for a microwave antenna.The microwave antenna is connected to a microwave generator by a coaxialcable, and is bonded within the antenna lumen. Microwave energy emittedby the antenna is capable of producing a cylindrically symmetricalradiation pattern which is concentrated about the antenna. Temperatureswithin a target area of the radiation pattern exceed about 45° C., whicheffectively necrose the irradiated tissue.

Cooling lumens, which communicate at a proximal end of the shaft,encircle the antenna lumen and are circumjacent an outer surface of theshaft. Water intake lumens adjacent the first side of the shaft arerelatively narrow in cross-section, while water exhaust lumens adjacenta second side of the shaft are relatively wide in cross-section. Cooledwater from a cooling system is pumped into the water intake lumens at adistal end of the shaft. The water flows to the proximal end of theshaft and returns to the cooling system via the water exhaust lumens.The water within the cooling lumens protects tissue immediately adjacentthe outer surface of the shaft when the antenna is energized byabsorbing heat energy from the adjacent tissue (i.e. thermalconduction). The water within the cooling lumens also alters theradiation pattern generated by the antenna by absorbing some of themicrowave energy emitted by the antenna. Water in the wider exhaustlumens near the second side of the shaft absorbs a greater amount ofmicrowave energy than water in the narrower intake lumens near the firstside of the shaft. As a result, the radiation pattern generated by themicrowave antenna (and therefore the pattern of thermal energydelivered) becomes asymmetrical, with a target area of tissue adjacentthe first side of the shaft being heated above about 45° C., and thetissue adjacent the second side of the shaft remaining below about 45°C.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a vertical sectional view of a male pelvic region showing theurinary organs affected by benign prostatic hyperplasia.

FIG. 2A is a side view of the distal end of the urethral catheter of thepresent invention.

FIG. 2B is an enlarged sectional view of the proximal end of theurethral catheter of the present invention.

FIG. 3 is a cross-sectional view of the urethral catheter of FIG. 2Btaken along line 3--3.

FIG. 4 is a perspective view of a proximal region of the urethralcatheter with the end portion taken in section from line 4--4 of FIG.2B.

FIG. 5 is an enlarged view of the male pelvic region of FIG. 1 showingthe urethral catheter of the present invention positioned within theprostate region.

FIG. 6 is a graph illustrating temperature distribution generated by thecatheter of the present invention as a function of time.

FIG. 7 is a partial sectional view of the microwave antenna of theurethral catheter of the present invention.

FIG. 8 is an exploded view of the microwave antenna shown in FIG. 7.

FIG. 9 is a block diagram of the transurethral microwave thermal therapysystem of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a vertical sectional view of a male pelvic region showing theeffect benign prostatic hyperplasia (BPH) has on the urinary organs.Urethra 10 is a duct leading from bladder 12, through prostate 14 andout orifice 16 of penis end 18. Benign tumorous tissue growth withinprostate 14 around urethra 10 causes constriction 20 of urethra 10,which interrupts the flow of urine from bladder 12 to orifice 16. Thetumorous tissue of prostate 14 which encroaches urethra 10 and causesconstriction 20 can be effectively removed by heating and necrosing theencroaching tumorous tissue. Ideally, with the present invention, onlyperiurethral tumorous tissue of prostate 14 anterior and lateral tourethra 10 is heated and necrosed to avoid unnecessary and undesirousdamage to urethra 10 and to adjacent healthy tissues, such asejaculatory duct 24 and rectum 26. A selective heating of benigntumorous tissue of prostate 14 (transurethral thermal therapy) is madepossible by microwave antenna-containing catheter 28 of the presentinvention, which is shown in FIGS. 2A and 2B.

FIG. 2A shows a side view of a distal end of catheter 28. FIG. 2B showsan enlarged sectional view of a proximal end of catheter 28. As shown inFIGS. 2A and 2B, catheter 28 generally includes multi-port manifold 30,multi-lumen shaft 32, shaft position retention balloon 34, connectionmanifold 35, cooling system 36 and microwave generating source 38.

Manifold 30 includes inflation port 40, urine drainage port 42,microwave antenna port 44, cooling fluid in port 46 and cooling fluidout port 48. Ports 40-48 communicate with corresponding lumens withinshaft 32. Manifold 30 is preferably made of medical-grade silicone soldby Dow Corning under the trademark Silastic Q-7-4850.

Shaft 32 is connected to manifold 30 at shaft distal end 50. Shaft 32 isa multi-lumen, Foley-type urethral catheter shaft which is extruded froma flexible, medical-grade silicone sold by Dow Corning under thetrademark Silastic Q-7-4850. Shaft 32, which has an outer diameter ofabout 16 French, includes outer surface 52, which is generallyelliptical in cross-section as shown in FIG. 3. Shaft 32 is long enoughto permit insertion of proximal shaft end 54 through urethra 10 and intobladder 12. In one preferred embodiment, shaft 32 is coated with ahydrophilic solution sold by Hydromer, Inc. under the mark Hydromer,which lubricates outer surface 52 of shaft 32 and facilitates itsadvancement within urethra 10.

As shown in FIGS. 2B-4, shaft 32 includes temperature sensing lumen 56,microwave antenna lumen 58, urine drainage lumen 60, balloon inflationlumen 62, cooling fluid intake lumens 64A and 64B, and cooling fluidexhaust lumens 66A and 66B. Lumens 56-66B generally extend from distalshaft end 50 to proximal shaft end 54.

Temperature sensing lumen 56 is positioned near first side 68 of shaft32. Temperature sensing lumen 56 communicates with microwave antennaport 44 and permits insertion of thermometry sensor 69 within shaft 32to monitor the temperature of surrounding tissue when shaft 32 isinserted within urethra 10. Sensor 69 exits through port 44 and isconnected through connection manifold 35 to urethral thermometry unit178B (shown in FIG. 9). In a preferred embodiment, thermometry sensor 69is a fiber optic luminescence type temperature sensor sold by LuxtronCorporation. Temperature sensing lumen 56 is sealed at proximal end 54by silicone plug 70.

Microwave antenna lumen 58 is eccentric to the longitudinal axis ofshaft 32, antenna lumen 58 being positioned nearer first side 68 ofshaft 32 than second side 72 of shaft 32. Antenna lumen 58 is sealed atproximal end 54 by silicone plug 70A. At its distal end, antenna lumen58 communicates with microwave antenna port 44. Microwave antenna 74 ispermanently positioned within antenna lumen 58 near balloon 34. Antenna74 is positioned within antenna lumen 58 so as to be generally situatedadjacent the benign tumorous tissue of prostate 14 when shaft 32 isproperly positioned within urethra 10. As shown in FIGS. 2A-2B, antenna74 is bonded within antenna lumen 58 by adhesive bond 75. Antenna 74 iscarried at the proximal-most end of coaxial cable 76. The distal-mostend of coaxial cable 76 is connected to connection manifold 35 by aconventional quick-coupling fitting 73. Coaxial cable 76 communicateswith microwave generating source 38 by connection cable 76A, which isconnected between microwave generating source 38 and connection manifold35. In one embodiment, connection cable 76A is a standard RG 400 coaxialcable. Microwave generating source 38 produces a maximum of 100 watts ofelectrical power at about 915 MHz frequency, +/- 13 MHz, which is withinthe FCC-ISM standards. When antenna 74 is energized by microwavegenerating source 38, antenna 74 emits electromagnetic energy whichcauses heating of tissue within prostate 14.

Urine drainage lumen 60 is positioned adjacent antenna lumen 58, betweenantenna lumen 58 and second side 72. Urine drainage lumen 60communicates with urine drainage port 42 and defines a drainage path forurine when proximal end 54 of shaft 32 is inserted within bladder 12.Urine drainage lumen 60 is connected to urine drainage lumen extension78 at proximal end 54. Urine drainage lumen extension 78 is bondedwithin proximal end cap 80. End cap 80 is further bonded over outersurface 52 of shaft 32 at proximal shaft end 54, with cavity 82surrounding lumen extension 78. With end cap 80 and urine drainage lumenextension 78 in place, opening 84 to lumen extension 78 permits urine todrain from bladder 12 through urine drainage lumen 60 and out urinedrainage port 42 when proximal shaft end 54 is inserted within bladder12. Drainage of urine from bladder 12 is necessary due to frequentbladder spasms which occur during transurethral thermal therapy.

Balloon inflation lumen 62 is positioned near second side 72, generallybetween urine drainage lumen 60 and second side 72. Balloon inflationlumen 62 communicates with inflation port 40 and is sealed at proximalend 54 by silicone plug 70B. Balloon inflation lumen 62 communicateswith interior 86 of balloon 34 by opening 88.

Balloon 34, which is formed from a tubular section of a flexible,medical-grade silicone sold by Dow Corning under the trademark SilasticQ-7-4720, is secured over shaft 32 by bonding balloon waists 90 and 92over exterior surface 52 of shaft 32 near proximal shaft end 54. Balloon34 is inflated by an inflation device 188 (shown in FIG. 9), which isconnected to inflation port 40 and which supplies positive fluidpressure to interior 86 of balloon 34. Balloon 34 is deflated wheninflation device 188 supplies a negative fluid pressure (i.e., a vacuum)to interior 86 of balloon 34. Balloon 34 serves to retain shaft 32 in afixed position within urethra 10 when balloon 34 is inflated withinbladder 12 near bladder neck 22, as shown in FIG. 5.

As shown in FIGS. 2B-4, cooling fluid intake lumens 64A, 64B arepositioned circumjacent first side 68, between first side 68 and antennalumen 58. Cooling fluid intake lumens 64A, 64B extend from distal shaftend 50 to proximal shaft end 54 where lumens 64A, 64B are exposed tocavity 82 of end cap 80. Intake lumens 64A, 64B are relatively narrow incross-section and have a relatively small cross-sectional surface area.Water contained within intake lumens 64A, 64B performs two essentialfunctions. First, water contained within lumens 64A, 64B absorbs some ofthe microwave energy emitted by antenna 74. This assists, in part, incontrolling the volume of tissue adjacent first side 68 of shaft 32 thatis heated above about 45° C. Second, the water within lumens 64A, 64Babsorbs heat energy generated by the microwave energy from adjacenttissues (i.e., urethra 10) via thermal conduction. This prevents theportion of urethra 10 adjacent first side 68 from being overheated anddamaged when antenna 74 is energized.

Cooling fluid exhaust lumens 66A, 66B are circumjacent second side 72with lumens 66A, 66B generally positioned between second side 72 andantenna lumen 58. Like intake lumens 64A, 64B, exhaust lumens 66A, 66Bextend from shaft distal end 50 to shaft proximal end 54 where exhaustlumens 66A, 66B are exposed to cavity 82 of end cap 80. Exhaust lumens66A, 66B are wider in cross-section than intake lumens 64A, 64B, andhave a cross-sectional area greater than the cross-sectional area ofintake lumens 64A, 64B. Water within exhaust lumens 66A, 66B istherefore capable of absorbing a greater amount of microwave energy whenantenna 74 is energized. As a result, for a given power output frommicrowave generating source 38, the temperature of tissue adjacentsecond side 72 will remain below about 45° C. Water within exhaustlumens 66A, 66B also absorbs heat energy from adjacent tissue (i.e.,urethra 10) when antenna 74 is energized, which prevents the portion ofurethra 10 adjacent second side 72 from being overheated and damagedwhen antenna 74 is energized.

Intake lumens 64A, 64B and exhaust lumens 66A, 66B are supplied withdeionized water from cooling system 36. Water from cooling system 36 ischilled to between about 12°-15° C. and pumped at a rate of betweenabout 100-150 milliliters per minute via water feed line 94A toconnection manifold 35. The water flows through connection manifold 35to water feed line 94B and to water intake port 46, which communicateswith water intake lumens 64A, 64B. Under fluid pressure, the watercirculates through intake lumens 64A, 64B to cavity 82 of end cap 80.The water returns to cooling system 36 through exhaust lumens 66A, 66Bto fluid exhaust port 48. The water is carried from water exhaust port48 via water return line 96B to connection manifold 35, and fromconnection manifold 35 to cooling system 36 via water return line 96A.The water is then re-chilled and re-circulated. Water feed line 94B andwater return line 96B are each provided with a conventionalquick-coupling fitting 65A and 65B, respectively, which permits catheter28 to be easily disconnected from cooling system 36.

FIG. 5 shows an enlarged view of the male pelvic region of FIG. 1 withcatheter 28 properly positioned within urethra 10. Orientation stripe 98along exterior surface 52 on first side 68, as shown in FIG. 4, ensuresthe proper orientation of shaft 32 within urethra 10. As shown in FIG.5, shaft 32 is positioned within urethra 10 with second side 72 of shaft32 oriented toward rectum 26. Water exhaust lumens 66A, 66B are orientedposteriorly, toward rectum 26 and water intake lumens 64A, 64B areoriented anteriorly toward fibromuscular tissue 100 of prostate 14. Theportion of transition zone 101 anterior and lateral to urethra 10 is themost frequent location of the tumorous tissue growth which causes BPH.Since water exhaust lumens 66A, 66B are capable of absorbing moremicrowave energy than water intake lumens 64A, 64B, the radiationpatterns created by microwave energy emitted from antenna 74 areasymmetrical. Thus, a relatively large volume of tissue enveloping theanterior portion of transition zone 101, adjacent first side 68, isheated to a temperature above about 45° C., which effectively necrosesthe tumorous tissue of prostate 14 which encroaches upon urethra 10. Incomparison, the temperature of tissue adjacent second side 72 remainsbelow about 45° C., thereby eliminating the harmful effects of themicrowave energy to ejaculatory duct 24 and rectum 26.

FIG. 6 is a graph which generally demonstrates a microwave thermaltherapy procedure and a temperature distribution which was generated bycatheter 28 of the present invention, with shaft 32 inserted into aPolyacrylamide gel formulation which simulates biological tissue. Theformulation and preparation procedures for the Polyacrylamide gel arediscussed in detail in D. Andreuccetti, M. Bini, A. Ignesti, R. Olmi, N.Rubino, and R. Vanni, Use of Polyacrylamide as a Tissue-EquivalentMaterial in the Microwave Range, 35 IEEE TRANSACTIONS ON BIOMEDICALENGINEERING 275 (No. 4, April 1988). FIG. 6 shows temperaturemeasurements taken from eight temperature sensors. Four sensors werealigned at fixed distances adjacent first side 68. Sensor 1A waspositioned immediately adjacent shaft 32; sensor 1B was positioned about0.66 cm from shaft 32; sensor 1C was positioned about 1.33 cm from shaft32; and sensor 1D was positioned about 2.0 cm from shaft 32.

Four sensors were also aligned at fixed distances adjacent second side72. Sensor 2A was positioned immediately adjacent shaft 32; sensor 2Bwas positioned about 0.66 cm from shaft 32; sensor 2C was positionedabout 1.33 cm from shaft 32; and sensor 2D was positioned about 2.0 cmfrom shaft 32.

The x-axis represents a relative period of time over which the microwavethermal therapy procedure was performed. The y-axis representstemperature in degrees Celsius, with horizontal line H representing 45°C. (the temperature at or above which cells are necrosed).

As generally shown in FIG. 6, the microwave thermal therapy procedure ofthe present invention includes five operating phases, P1-P5. Lines 1A-1Dand 2A-2D correspond with sensors 1A-1D and 2A-2D, respectfully. Duringfirst phase P1, cooling system 36 is turned on and chilled water ispumped through cooling lumens 64A, 64B and 66A, 66B. A drop intemperature immediately adjacent shaft 32 is represented by lines 1A,2A. At the end of first phase P1, cooling system 36 is turned off. Atthe beginning of second phase P2, a relatively small amount of power(about 5 watts) is applied to microwave antenna 74. The temperatureimmediately adjacent shaft 32 rises asymmetrically due to the greaterabsorptivity of water in the larger exhaust lumens 66A, 66B on secondside 72, as shown by lines 1A, 2A. The power is applied long enough tomerely warm adjacent tissue to about 40° C. By the end of second phaseP2, temperatures generally return to base line temperature.

In a preferred embodiment of the present invention, the tissue responsesto the chilling during P1 and the heating during P2 aid in determiningthe vascularity of the tissue to be treated. This information aids indetermining the amount of power necessary to treat tumorous tissue ofprostate 14.

At the beginning of third phase P3, cooling system 36 is again turned onthereby pumping chilled water through cooling lumens 64A-66B. Thetemperature immediately adjacent shaft 32 correspondingly drops asindicated by lines 1A, 2A. Prechilling of the tissue immediatelyadjacent shaft 32 aids in protecting the tissues immediately adjacentshaft 32 (i.e., urethra 10) from overheating due to a relatively rapidapplication of power from antenna 74.

Microwave generating source 38 is again turned on at the beginning offourth phase P4 at a sustained power output of about 20 watts. As shownin FIG. 6, due to the absorptivity differential between water in thenarrower intake lumens 64A, 64B and water in the wider exhaust lumens66A, 66B, temperatures adjacent second side 72, represented by lines2A-2D, are cooler than temperatures adjacent first side 68, representedby lines 1A-1D. The temperature differentials are most profound within atarget volume of tissue 0.66 cm from shaft 32. Within this targetvolume, as shown by lines 1A, 2A and 1B, 2B, the difference intemperature from first side 68 and second side 72 is on the order ofabout 10° C. Thus, by adjusting cooling system parameters or poweroutput from microwave generating source 38, tissue within 0.66 cm offirst side 68 can be heated to temperatures at or above about 45° C.,while tissue within 0.66 cm of second side 72 can remain at temperaturessubstantially below 45° C. In this manner, tissue-necrosing temperatureswithin the target volume are essentially restricted only to tissue nearfirst side 68, which is the most frequent location of periurethraltumorous prostatic tissue. Alternatively, by adjusting the power outputor cooling system parameters, a relatively small volume of tissueadjacent second side 72 can be heated above about 45° C. to necrose someof the tumorous prostatic tissue which is posterior and lateral to theurethra. In the preferred embodiment, during fourth phase P4, microwavegenerating source 38 is operated for at least about 45 minutes.

As shown by lines 1A, 2A, during P4, the temperature of tissueimmediately adjacent shaft 32 (which is representative of temperaturesof urethra 10), as well as temperatures of tissue beyond 0.66 cm fromshaft 32, as shown by lines 1C, 2C and 1D, 2D, are maintainable wellbelow 45° C. This is accomplished by adjusting cooling system parametersand, if necessary, power output from microwave generating source 38.

At the end of fourth phase P4 power is turned off. At the beginning offifth phase P5, cooling system 36 continues to operate, circulatingwater through cooling lumens 64A-66B. A temperature drop immediatelyadjacent shaft 32 is relatively rapid as shown by lines 1A, 2A withinP5. In a preferred embodiment of the present invention, cooling system36 continues to operate for a period of time (on the order of 10 to 120minutes) after the procedure to cool urethra 10 and reduce edemaresulting from the application of heat to the periurethral tissues ofprostate 14. In an alternative embodiment, water feed line 94B, waterreturn line 96B and thermometry sensor 69 (as shown in FIG. 2A) aredisconnected from connection manifold 35. Water feed line 94B and waterreturn line 96B of catheter 28 are then connected to another coolingsystem similar to cooling system 36 and water is then circulated throughcooling lumens 64A-66B in a manner similar to that previously described.In this fashion, recovery from the previously described procedure can beaccomplished away from the treatment area thereby enabling microwavegenerating source 38 and cooling system 36 to be readily available fortreatment of another patient.

FIG. 7 shows a partial sectional view of microwave antenna 74 of thepresent invention. Antenna 74 is positioned at a proximal-most end ofshielded coaxial cable 76. Cable 76 is a standard RG 178U coaxial cableand includes inner conductor 120, inner insulator 122, outer conductor124, and outer insulator 126. Outer insulator 126, outer conductor 124and inner insulator 122 are stripped away to expose about 3 millimetersof outer conductor 124, about 1 millimeter of inner insulator 126 andabout 1 millimeter of inner conductor 120. Capacitor 128 includes firstend 130, which is connected to inner conductor 120 by soldering, andsecond end 132, which connects to antenna 74. Capacitor 128 serves tocounteract a reactive component of antenna 74, thereby providing a 50ohm match between coaxial cable 76 and microwave generating source 38,and antenna 74.

Tubular extension 134, which is a hollow section of outer insulator 126of coaxial cable 76, is positioned over capacitor 128 and the exposedlength of inner insulator 122 and secured by bond 136. Tubular extension134 includes hole 138, which provides an exit for second end 132 ofcapacitor 128. Wound about outer insulator 126 and tubular extension 134is flat wire 140. Flat wire 140 is a single piece of flat copper wirewith dimensions of about 0.009 inch by about 0.032 inch incross-section, which provides a relatively large surface area formaximum current flow while minimizing the cross-sectional size ofantenna 74.

FIG. 8 is an exploded view of a portion of antenna 74 which shows itshelical dipole construction. Generally, the efficiency of any dipoleantenna is greatest when the effective electrical length of the antennais generally one half the wavelength of the radiation emitted in thesurrounding medium. Accordingly, a relatively efficient simple dipoleantenna, operating at about 915 MHz, would require a physical length ofabout 8 centimeters which, according to the present invention, wouldneedlessly irradiate and damage healthy tissue. Furthermore, thephysical length of a relatively efficient simple dipole antennaoperating at about 915 MHz cannot be varied.

As shown in FIG. 8, flat wire 140 is soldered to outer conductor 124 atsolder point 146. Flat wire 140 is then wound in a distal directionabout outer insulator 126 and in a proximal direction about tubularextension 134, thereby forming first wire section 142 and second wiresection 144, both of which are of equal length. In one embodiment, firstand second wire sections 142 and 144 are each comprised of eight,equally-spaced windings of flat wire 140. The combined length of firstand second wire sections 142 and 144, and hence the overall length ofantenna 74, ranges from about 1.5 centimeters to about 4.0 centimeters,and varies according to the length of the area of prostate 14 whichrequires treatment. A standard medical-grade silicone tube (not shown),which has been allowed to soak in a solvent, such as Freon, ispositioned over first and second wire sections 142 and 144. As thesolvent evaporates, the silicone tube shrinks, thereby securing flatwire 140 to outer insulator 126 and tubular extension 134.

The helical dipole construction of the present invention, allows antenna74 to range in physical length from about 1.5 to 4 centimeters, whileelectrically behaving like an eight centimeter-long simple dipoleantenna. In other words, antenna 74 has an effective electrical lengthgenerally equal to one half of the wavelength of the radiation emittedin the surrounding medium, independent of its physical length. Forpurposes of definition, the surrounding medium includes the cathetershaft and the surrounding tissue. This is accomplished by varying thenumber and pitch of the windings of first and second wire sections 142and 144. A family of catheters, which contain relatively efficienthelical dipole antennas of different physical lengths, permits selectionof the antenna best suited for the particular treatment area. Inaddition, antenna 74 of the present invention is capable of producing aconstant heating pattern in tissue, concentrated about antenna 74,independent of the depth of insertion into the tissue.

Second end 132 of capacitor 128, which exits hole 138, is soldered tosecond wire section 144 at tap point 148, as shown in FIG. 7. Tap point148 is a point at which the resistive component of the combinedimpedance of first wire section 142 and second wire section 144 matchesthe characteristic impedance of coaxial cable 76. The impedance ofeither first wire section 142 or second wire section 144 is expressed asZ, where Z=R+jX. The impedance Z varies from a low value at solder point146 to a high value at a point farthest from solder point 146. Thereexists a tap position where R is equal to 50 ohms, but an imaginarycomponent, X, is inductive. This inductive component can be canceled byinserting a series capacitance, such as capacitor 128, which has a valueof -jX ohms. This results in an impedance match of 50 ohms real. Theresulting method of feeding antenna 74 is commonly called gammamatching. In one embodiment of the present invention, where the physicallength of flat wire 140 is about 2.8 cm, tap point 148 is about 3.5turns from solder point 146 on second wire section 144. In the preferredembodiment, the value of capacitor 128 is about 2.7 pF.

The helical dipole construction of antenna 74 achieves a relativelysmall size, which permits intraurethral application. The helical dipoleconstruction is also responsible for three features which enable antenna74 to achieve greater efficiency than prior known interstitial microwaveantennas: good impedance matching, good current carrying capability andan effective electrical length which is generally one half of thewavelength of the radiation emitted in the surrounding medium,independent of the physical length of antenna 74.

First, the good impedance match between antenna 74 and inner conductor120 minimizes reflective losses of antenna 74, with measured reflectivelosses of less than 1% in a preferred embodiment. Second, the use offlat ribbon wire 140 for first wire section 142 and second wire section144 minimizes resistive losses of antenna 74 by providing a greatersurface area upon which RF current can be carried. Finally, the helicaldipole design of antenna 74 has an effective electrical length which isgenerally one half of the wavelength of the radiation emitted in thesurrounding medium, independent of the physical length of antenna 74.This permits the physical length of antenna 74 to be varied toaccommodate varying sizes of individual prostates while maintaining thesame efficient, effective electrical length of antenna 74.

The use of an efficient microwave antenna is critical to the ability tofocus thermal energy a distance from the antenna within a target volume.An inefficient antenna produces a lesser intensity of microwaveradiation within the target volume than desired. It also producesundesired heat close to the urethra, which will damage the urethra ifnot carried away by an increased coolant flow. This added burden on thecooling system reduces its capacity to protect the urethra, therebylimiting the microwave power that can be radiated without elevatingurethra temperatures above safety limits. With microwave power limitedby cooling system capacity, the heat delivered to the desired targetarea of the prostate will not be sufficient for effective therapy. Theefficient helical dipole design of antenna 74 of the present invention,however, ensures that almost all heat delivered during the treatment isdelivered in the form of microwave energy, rather than conductive heatenergy.

FIG. 9 is a block diagram of transurethral microwave thermal therapysystem 170, with which urethral catheter 28 is used. System 170 includescooling system 36 microwave generating source 38, user interface 172,real time controller (RTC) 174, directional coupler 176, thermometrysensors 182 and 184, coolant pressure sensor 186, balloon inflationdevice 188, and urine collection container 190.

As shown in FIG. 9, control of microwave generating source 38 andcooling system 36 is effected by real time controller 174, which is inturn controlled by user interface 172. User interface 172 is an IBMcompatible machine containing two hard drives for data storage: one forbackup, and one for normal operation of system 170. User interface 172communicates with RTC 174, which is responsible for all closed loopfeedback to run system 170. RTC 174 has direct closed loop control ofmicrowave power from microwave generating source 38, and coolant flowand coolant temperature of cooling system 36. Closed loop feedbacktracks out variations in gain, drift and cable losses inherent inmicrowave generating source 38, and variability in pump output andrefrigeration system efficiency of cooling system 36. In addition tomonitoring microwave generating source 38 and cooling system 36, RTC 174also monitors and controls several channels of thermometry via inputsfrom thermometry unit 178. Cooling system thermometry 178A measures thecoolant and chiller temperatures based upon signals from coolanttemperature sensors 182 and 184 and a chiller temperature sensor (notshown) of cooling system 36. Urethral thermometry 178B measures urethraltemperature based upon signals from temperature sensor 69 withincatheter 28. Rectal thermometry 178C measures rectal temperature basedupon signals received from a sensor (not shown) within rectal probe 180.

RTC 174 transmits all closed-loop feedback to user interface 172, whichprocesses the input and transmits corrections and instructions back toRTC 174. RTC 174 interprets the instructions given to it by processcontrol language received from user interface 172 and executes theinstructions in real time. All corrections from user interface 172 aremade to maintain a given thermal profile throughout the transurethralthermal therapy. In addition, system 170 includes a hardware fail-safecircuit which shuts down system 170 should any parameter fall outside agiven range of values.

While the beneficial uses of the microwave antenna-containing catheterof the present invention have been described with respect to theurethra, other intracavitary applications are implied.

Although the present invention has been described with reference topreferred embodiments, workers skilled in the art will recognize thatchanges may be made in form and detail without departing from the spiritand scope of the invention.

What is claimed is:
 1. A device for administering therapy to a prostatecomprising:a urological catheter; and heating means within the catheterfor selectively delivering heat to the prostate, wherein the heatingmeans is capable of delivering a first amount of heat in a first radialdirection which is greater than a second amount of heat in a secondradial direction.
 2. A device for administering thermal therapy toprostatic tissue comprising:a urological catheter; heating means withinthe catheter for selectively heating the prostatic tissue, the heatingmeans capable of delivering heat in a first volume of prostatic tissuewhich is greater than that delivered to a second volume of prostatictissue.
 3. An intraurethral device for treating a prostate comprising:aurological catheter; and electromagnetic energy emitting means withinthe catheter for selectively directing electromagnetic energy into theprostate, the electromagnetic energy emitting means capable ofdelivering first amount of energy in a first radial direction relativeto the catheter which is greater than a second amount of energydelivered in a second radial direction relative to the catheter.
 4. Amethod of treating the prostate comprising:inserting into a urethra aurological catheter which contains a heating system; activating theheating system to produce a first amount of heat in a first radialvolume of the prostate and to produce a second amount of heat in asecond radial volume of the prostate, the first amount of heat beinggreater than the second amount of heat.